Hmb Exam 2 Structure And Infection Cycle Of Viruses

Front 1

ebola virus

Back 1

very virulent, causes death readily

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rhinovirus

Back 2

common cold virus

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bacteriophage

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virus that infects bateria only and cannot infect any other cells

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rabies virus

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has genetic material in the middle

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most infections are__________

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viruses (have viral origin)

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virus was discovered after bacteria in is much___________than bacteria

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smaller (microscopic)

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virus comes originates from the latin and mean___________or___________

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toxin
poison

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Genetic material of a virus

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contains RNA or DNA (bacteria only has DNA)

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genetic material of virus is surrounded by a__________________coat

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protein, lipid or glycoprotein

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a virus obligates an _______________organism

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intracellular

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in order for a virus to survive it has to get into_________

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the host cell

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a virus takes over the host cell in order to_____________

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reproduce - they change the host cell which allows them to reproduce and replicate

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the main goal of a virus is_________ and therefore needs to get into the host cell to replicate

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survival

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every drop of seawater has more than____________viral particles

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a million

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we carry viral genomes as part of our___________________

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genetic makeup

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viruses infect

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pets, domestic food animals, wildlife, plants, insects

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the majority of viruses infecting us have no effect because our __________________ fight them

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immune system

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retroviral DNA

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8% of our genetic makeup are of viral origin

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endogenous retroviruses

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each person has thousands of new and old retrovirus genomes integrated into our DNA

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HIV is an example of a_________________but not all of these cause disease

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retrovirus

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viruses are genetic material and contain a _______________code

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protein

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3 theories on the origin of viruses

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1. regressive evolution (dont have to have all genes - can steal genes to metabolize)
2. cellular origins (some evidence - some viruses have similar structures than cells)
3. independent entities (evolved differently from cells - exist on their own)

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regressive evolution

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viruses are DEGENERATE life-forms which have lost many functions that other organisms possess and have only retained the genetic information essential to their parasitic way of life

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cellular origins

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viruses are sub-cellular, functional assemblies of macromolecules which have escaped their origins inside cells (contain possible truth)

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independent entities

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viruses evolved on a parallel course to cellular organisms from self replicating molecules (contain possible truth)

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ancient egypt first record of virus infection____________ - paralytic poliomyelitis which is_________________

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3700BC
muscle weakness and paralysis

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Pharaoh Siphtah (1200-1193 BC) had_____________ and Pharaoh Rameses (1196 BC) had ______________

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polio virus
small pox virus

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in China (1196 BC)______________was an endemic and _____________was developed

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smallpox
variolation

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variolation

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inhalation of dried crusts from smallpox lesion, or inoculation of the pus from a lesion into a scratch on he forearm of a child

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reason for variolation

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by introducing a small part of the virus to people in order to build an immunity against it

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in england (1796)_______________ created a vaccine for smallpox

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Edward Jenner - found that milkmaids were immune to smallpox bc they handled cows (that had cow pox) which made them immune (cow pox are less virulent than small pox - just blister)

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on Feb 12 1892,________________, a russian botanist showed that extracts from diseased tobacco plants could transmit disease to other plants after passage through____________fine enough to retain the smallest known bacteria

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Dmitri Iwanowski
ceramic filters

ex Tobacco mosaic virus (breaks in plants)

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viruses can infect different types of cells:

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bacteria (bacteriophages)
Plant cells
animal cells (incl human cells)

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viruses are specific to a specific ________ type and are obligate_______________ parasites

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cell
intracellular

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virion

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the intact virus particle

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virion structure must overcome 2 basic problems:

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1. must be strong enough to protect the viral nucleic acid
2. must be able to release the viral nucleic acid for infection

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the virion has 4 components

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1. genetic material
2. caspid (protein)
3. envelope
4. glycoproteins

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viruses are grouped according to the type of genetic material they contain:

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DNA viruses ex. HSV (herpes simplex virus)
RNA viruses ex. HIV (human immunodeficiency virus)

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DNA and RNA viruses are_____________similar

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structurally

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caspid

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protein coat surrounding the viral nucleic acid

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each caspid is made up of subunits called_______________ which bond together and give the caspid________________.

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capsomeres
structural symmetry

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viruses posses either ____________or ____________ symmetry

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helical ex. tobacco mosaic, rabies, ebola virus
icosahedral ex. rhinovirus

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many viruses that infect humans and other animals are______________

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enveloped

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viral envelope: virion gets wrapped in ____________________upon movement out of the host cell

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host membranes

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envelopes form when viral_______________ associate with the __________________of the host cell

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glycoproteins
plasma membrane

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all envelopes have a _______________bilayer

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phospholipid

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envelope ______________ are firmly embedded in the envelope bilayer

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glycoproteins

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envelope glycoproteins can form_________or other structures on the outside of the virion which can be used to ____________ via receptors on host cell

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spikes
attach to a host cell

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In virion: capsomere

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protein molecule forming caspid

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In virion: caspid (protein coat)

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protein shell surrounding nucleic acd

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In virion: nucleocaspid

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nucleic acid plus caspid

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In virion: envelope (viral membrane)

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phospholipid bilayer embedded glycoproteins surrounding caspid in enveloped virus

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virion (viral particle)

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complete infectious viral structure: nucleic acid plus capsid for non-enveloped virus; nucleic acid plus capsid plus envelope for enveloped virus

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he goal of a virus is survival by taking advantage of the____________resources to replicate and produce___________

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host's
progeny (descendants)

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animal viruses can be either___________ or ____________

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lytic
lysogenic

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lytic infection

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cells die upon release of progeny virus

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lysogenic (latent) infection

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virus is quiescent (inactive) in host - no obvious disease, virus genetic material transcriptionally silent, incorporation of virus genome in host cell DNA
ex. herpes virus (not always active)

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herpes simplex virus (HSV) has a __________and _____________stages of infection: HSV 1 and HSV 2

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lytic
lysogenic

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HSV is ubiquitous and contagious, transmitted via_____________ - may be transmitted____________during childbirth

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contact
verically

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HSV produces___________ on the skin and___________of lips, mouth and genital areas

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blisters
mucous membranes

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How long does a person have the herpes virus

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their lifetime ( not always active)

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not all viruses go through_____________ cycle of infection

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latent
ex. influenza (rhinovirus)

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it is advantageous for a virus to undergo latency because:

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latent infection has important implications for virus survival and transmission - virus is part of host for life and usually transmitted silently

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in animal cells there are 6 steps in lytic infection:

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1. attachment
2. penetration
3. uncoating
4. biosynthesis
5. maturation
6. release

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viruses dont have movement, they depend on_____________________to spread

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replication of cells

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viruses gain entry into plant cells by __________in plants, because viruses don't have glucoproteins or envelopes or a plasma membrane.

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breaks

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viruses spread through_____________ and _____________ of plant cell wal

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plasmodesmata
phloem

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bacteriophages are injected through the ___________by utilizing features on the outer surface of prokaryotic cells such as _________________

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cell wall
lipopolysaccharides and glycoproteins

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bacteriophages transport____________ and______________

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machinery
sex pili

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in order for a virus to replicate and spread new________ must be made - synthesis of viral proteins and new viral genomes

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virions

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synthesis and location of viral products depend on whether viruses contain

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DNA
RNA

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RNA viruses usually replicate in the_______________

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cytoplasm

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DNA viruses usually replicate in the ____________

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nucleus

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negative strand________virus is complimentary to__________

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DNA
mRNA

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positive strand________ virus is equivalent to_______________

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RNA
mRNA

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viruses need to synthesize new_____________and new_____________ in order to replicate

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genomes
viral proteins

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Double-stranded DNA viruses (herpesvirus, poxviruses, papillomaviruses) use the same________________ as the host cell for biosynthesis

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mechanisms

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biosynthesis

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1.DNA is replicated to make new viral genomes
2. one strand of viral DNA is transcribed into mRNA (using the host cell or viral RNA polymerase) to make viral proteins)

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The host may not have everything the virus need to replicate, so the virus________________

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brings some of its own material ex viral RNA polymerase

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In RNA viruses, mechanisms of biosynthesis are more___________ than in RNA viruses

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complicated

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viruses must carry/express their own __________________ that is required to make RNA from viral mRNA in order to replicate________________

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RNA dependent RNA polymerases
genomes

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double stranded RNA viruses (ex.rotavirus, gastroenteritis) contain one _________strand (mRNA) and one__________strand

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positive
negative (complimentary to the positive strand)

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single stranded RNA viruses are either______________stranded or _____________stranded

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positive (contain positive strand)
negative (contain a negative strand)

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in double-stranded RNA viruses, during infection the ____________strand is copied into messenger RNA by __________________ and the mRNA is used to produce_________________

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negative
viral RNA polymerase
viral proteins

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each of the strands and in RNA virus is used as a_________________to make a new double-stranded genome

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template

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retroviruses are RNA viruses that contain_________________

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reverse transcriptase

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reverse transcriptase converts__________into___________

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RNA into DNA

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converted viral____________(from reverse transcriptase in retroviruses) can be inserted into the host cell_____________

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DNA
chromosome

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retroviruses cause________________infection

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latent

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during virus replication: host___________________is inhibited by the virus

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DNA synthesis (all polymerases and proteins concentrate on viral DNA synthesis)

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during virus replication: host_______________and _____________is shut down

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transcription and translation

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during virus replication: transcription machinery may be _________________for use by virus

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stolen or modified

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during virus replication: viruses are completely reliant on host___________________

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translational machinery - may be altered for use of virus

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during virus replication: specialized__________ of virus replication form in cells (DNA viruses)

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sites

"viral factories" are created

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during virus replication: viral factories contain

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DNA templates, viral replication machinery and machinery necessary for gene expression (transcription and translation machinery)

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maturation

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involves the movement of newly made viral components to specific sites in the host cell

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2 steps of maturation

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1. intracellular trafficking
2. assembly

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intracellular trafficking

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transport of viral components to virus assembly sites

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many_____________ viruses assemble near the host cell membrane - others assemble near membrane bound organelles

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enveloped

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___________________viruses assemble in the host cell nucleus

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non-enveloped

Front 101

new virions can be released from the host cell in 2 ways:

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1. lysis - non-enveloped viruses (causes death of cells)
2. budding - enveloped viruses (cells are not compromised for a while)

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viruses can spread form cell to cell by using ______________ between cells and can aslo spread through the formation of ______________

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tight junctions
syncytia

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syncytia

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allow movement through the body without exposure to the immune system

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viral host cell interactions occur through random________________

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collisions

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the ____________is important to determine whether infection occurs, ___________infections produce the maximum number of virions

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number of viruses
lytic

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viruses can be_____________or ______________for cells depending on receptor requirement

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"promiscuos" or highly specific

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host cell must be_______________for infection to succeed (must contain all components required to make new virions)

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permissive

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viral infections at the apical cell surface usually cause____________infection

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acute

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viral infection at the basolateral cell surface can become______________

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systemic

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many viruses only attach only to specific areas of the host cell membrane known as ___________

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lipid rafts

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lipid rafts

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rich in cholesterol, fatty acids and other lipids - may contribute to stable attachment of several viruses and site of release for many viruses